Monday, November 30, 2009

That is the question that is being asked in this review of the effort to incorporate gravity into quantum mechanics (the full paper is available for free, upon registration, during the first 30 days of online publication)[1].

Abstract: I give a pedagogical explanation of what it is about quantization that makes general relativity go from being a nearly perfect classical theory to a very problematic quantum one. I also explain why some quantization of gravity is unavoidable, why quantum field theories have divergences, why the divergences of quantum general relativity are worse than those of the other forces, what physicists think this means and what they might do with a consistent theory of quantum gravity if they had one. Finally, I discuss the quantum gravitational data that have recently become available from cosmology.

Launchball is a physics puzzler where you need to get a ball from Point A to Point B using the tools at hand. These tools include fans, magnets, tesla coils, bunsen burners and much more. Each tool is introduced in sequential fashion during the introductory levels and in general feels much more accessible than similar games we've played. Once you set up the board as you want, you can press "start" to set the scene in motion to see if you've succeeded.

Saturday, November 28, 2009

New tools will link papers by concepts, not just by the citations they contain, and this will help users without advanced expertise -- including some outside the scientific community -- understand the significance of new research, said Ginsparg.

I wonder if they'll put in new efforts to weed out some of the "strange" papers (I'll refrain from calling them crackpottery) that appear periodically.

Leggett said, "We can all tell when a movie of some everyday event, such as a kettle boiling or a glass shattering, is run backwards.

"Similarly, we all feel that we can remember the past and affect the future, not vice versa. So there is a very clear "arrow" ( direction ) of time built into our interpretation of our everyday experience.

"Yet the fundamental microscopic laws of physics, be they classical or quantum-mechanical, look exactly the same if the direction of time is reversed. So what is the origin of the "arrow" of time?

"This is one of the deepest questions in physics; I will review some relevant considerations, but do not pretend to give a complete answer."

It took place on Nov. 27 (yesterday). Did anyone reading this attended this lecture? If you did, I'd appreciate a brief report.

Albert HUBO is an android robot. It is composed of a head, which takes after Dr. Albert Einstein, and HUBO’s body. The development period took about 3 months, and it had been finished at November, 2005. The head part was developed by Hanson-Robotics. Its skin is a special material, Frubber, often used at Hollywood.

Besides being rather creepy, it is in poor tastes because as most of us know, Einstein's brain was removed from his head. Now with this thing, it appears as if his head has been decapitated from his body and put on this robot.

Monday, November 23, 2009

Geneva, 23 November 2009. Today the LHC circulated two beams simultaneously for the first time, allowing the operators to test the synchronization of the beams and giving the experiments their first chance to look for proton-proton collisions. With just one bunch of particles circulating in each direction, the beams can be made to cross in up to two places in the ring. From early in the afternoon, the beams were made to cross at points 1 and 5, home to the ATLAS and CMS detectors, both of which were on the lookout for collisions. Later, beams crossed at points 2 and 8, ALICE and LHCb.

"It's a great achievement to have come this far in so short a time," said CERN Director General Rolf Heuer. "But we need to keep a sense of perspective - there's still much to do before we can start the LHC physics programme."

Beams were first tuned to produce collisions in the ATLAS detector, which recorded its first candidate for collisions at 14:22 this afternoon. Later, the beams were optimised for CMS. In the evening, ALICE had the first optimisation, followed by LHCb.

"This is great news, the start of a fantastic era of physics and hopefully discoveries after 20 years' work by the international community to build a machine and detectors of unprecedented complexity and performance," said ATLAS spokesperson Fabiola Gianotti.

"The events so far mark the start of the second half of this incredible voyage of discovery of the secrets of nature," said CMS spokesperson Tejinder Virdee.

"It was standing room only in the ALICE control room and cheers erupted with the first collisions," said ALICE spokesperson Jurgen Schukraft. "This is simply tremendous."

"The tracks we're seeing are beautiful," said LHCb spokesperson Andrei Golutvin, "we're all ready for serious data taking in a few days time."

These developments come just three days after the LHC restart, demonstrating the excellent performance of the beam control system. Since the start-up, the operators have been circulating beams around the ring alternately in one direction and then the other at the injection energy of 450 GeV. The beam lifetime has gradually been increased to 10 hours, and today beams have been circulating simultaneously in both directions, still at the injection energy.

Next on the schedule is an intense commissioning phase aimed at increasing the beam intensity and accelerating the beams. All being well, by Christmas, the LHC should reach 1.2 TeV per beam, and have provided good quantities of collision data for the experiments' calibrations.

These are just too morbid and gruesome for me. First it was Einstein's brain, now it's Galileo's fingers. It seems that they found his "missing" fingers after more than 100 years.

Removing body parts from the corpse was an echo of a practice common with saints, whose digits, tongues and organs were revered by Catholics as relics with sacred powers.

There is an irony in Galileo's having been subjected to the same treatment, since he was persecuted by the Catholic Church for advocating the theory that the earth circles the sun, rather than the other way around. The Inquisition forced him to recant, and jailed him in 1634.

The people who cut off his fingers essentially considered him a secular saint, Galluzzi said, noting the fingers that were removed were the ones he would have used to hold a pen.

Horrors! People need to really find a hobby!

Ironically, they found the fingers during the 2009 Year of Astronomy commemorating Galileo! Can't stage this any better!

I was planning on doing quite a bit of work this morning when I showed up extra early at the lab, but instead, I spent several delightful minutes reading this amazing personal account of the Manhattan Project and the dropping of the bombs that ended World War II. This personal account was written by Lawrence Bartell, one of the last remaining participants of the venerable project.

Abstract: A personal account of work on the Manhattan Project in Chicago by one of the few remaining survivors of the war-time project is given, illustrating, among other things, how absurd things can happen at a time of great stress and concern.. As is well known, Los Alamos was the site specializing in the physics of the bomb while Chicago emphasized metallurgical and chemical research. Nevertheless, physics played a significant role in Chicago, as well. That is where Fermi constructed the worlds first uranium pile under the stands of Stagg field, a site at which this author got seriously irradiated. Some curious events occurring after the bomb was dropped are also related. In addition, at this time of public protest by sincere people who question the ethics of America for dropping the bomb on innocent civilians, certain facts, obviously unknown to the protesters, are presented which place the bombing in a rather different light.

It's amazing that all of the radiation and chemical exposure that he endured haven't caused him more significant health problems.

It's an amazing historical account and adds another perspective to the Manhattan Project, especially from the Chicago effort.

Albert Crewe, the inventor of the scanning transmission electron microscope, and the first person to image single atoms, died this past week.

Dr. Crewe's breakthrough image of an atom was taken in 1970 with a scanning transmission electron microscope of his own invention at the U. of C., where he taught until 1996.

The uranium and thorium atoms that Dr. Crewe captured were magnified 1 million times. It was a significant breakthrough -- an atom is incredibly tiny, approximately 4 billionths of an inch in diameter. The event was met with quiet satisfaction by Dr. Crewe and his fellow Hyde Park physicists.

Again, this is one of those giants in the field that many in the public would not know, but whose work has such huge impact on our lives. Thank you, Dr. Crewe!

There is a very good review article in the latest issue of Science[1] that compiles all of our experimental and theoretical understanding of light propagation in a medium.

Abstract: It is now possible to exercise a high degree of control over the velocity at which light pulses pass through material media. This velocity, known as the group velocity, can be made to be very different from the speed of light in a vacuum c. Specifically, the group velocity of light can be made much smaller than c, greater than c, or even negative. We present a survey of methods for establishing extreme values of the group velocity, concentrating especially on methods that work in room-temperature solids. We also describe some applications of slow light.

The more complete story on this can be found at Times Online. The part I found to be quite hilarious was this:

How did she become a prostitute? She studied anthropology and mathematics in Florida: “I wanted to be a physicist, but that just didn’t work out.” After Florida, her family lived in Sheffield, where she studied some more: “By the time I got to Sheffield it was for doctoral study at the department of forensic pathology.”

Wednesday, November 18, 2009

Paul Chu, after serving as president of the Hong Kong University of Science and Technology, returns to the scene of his triumph at the University of Houston. Back in the heyday of high-Tc superconductors, he discovered YBCO after the publication of Bednorz and Müller's LACO, the first high-Tc superconductor. What was significant about YBCO was that it was the first superconductor discovered that has a Tc above liquid nitrogen temperature. This is important because it allows one to have a superconductor using a relatively cheap cooling source, rather than using liquid helium.

This, of course, was the trigger for the "Physics Woodstock" at the 1987 APS March Meeting in New York. Ah, the good old days!

Tuesday, November 17, 2009

I don't normally find reading papers on quantum gravity to be "entertaining". However, this is actually is, simply because the authors have to be rather concise due to limited space. Written by Sabine Hossenfelder Lee Smolin of the Perimeter Institute, it actually provides quite an overview of the phenomenological aspect of the search for the effects of quantum gravity. It focuses entirely on what we had measured and can possibly measure in the next decade or so. Reading this, one notices a lot of "negative result" experiments, especially on the search for possible violations of Special Relativity at those extreme scales.

This is an excellent review article by John Pendry on left-handed material and its application to "cloaking". Pendry, as everyone should already know, revived this field of study with his work on metamaterial. So this article compliments quite well with the earlier article in Physics Today.

The film - previously called Schrodinger's Girl - centres on Rebecca Hunter, a disgraced scientist conducting research into alternate universes. She discovers a way to travel between realities and then finds her parallel-world counterparts have their own agendas: Anastacia Hunter is the science director for a gulag in the People's Republic of Great Britain, while Sarah Hunter-Gibson is a professor in a utopian hi-tech society.

Rebecca takes a terrifying trip into the People's Republic, a dystopian alternative Britain, where her encounter with a totalitarian regime is only the beginning of her problems as the multiverse begins to unravel around her. She has to use her sharp intellect and mastery of quantum physics to save the entire universe.

Oy vey!! :)

Well, to be fair, I shouldn't make any comments on this since I haven't seen it. And it is, after all, a "sci-fi" movie, so they should have some latitude to run away with it a bit. But this parallel universe type of theme is nothing new. How come no one makes a movie about the possibility of fractionalization and spin-charge separation, for example? Now THAT would be entirely new! :)

Monday, November 16, 2009

This is another fun article, and fun physics, that could be of interest to many casual reader. It's a very in-depth analysis of the trajectory of a soccer ball, with and without spin. The paper has been published in the Dec. 2009 issue of AJP.

You have a thin film that's already semi-transparent. If you punch more holes into the film, do you expect more light to get through? You would, wouldn't you? That's not what happened here!

Toward this end, researchers from the University of Stuttgart in Germany laid very thin films of gold onto pieces of glass and then used ion beams to etch the film with holes arranged in a regular, square array. These holes were smaller than the wavelength of light and, despite being so tiny, are just the kind of openings that have been shown to let light through the thicker, opaque film used in the 1998 experiment. But in the new experiment, the gold film was so thin--only 20 nanometers--that light could already shine through it. And surprisingly, less light went through the holey gold than through the original semitransparent film.

You have to read the rest of the article (and maybe even the paper) to find out why. This, btw, is another example of some of the most fascinating results out of condensed matter.

Friday, November 13, 2009

"I have been thinking about how I can make use of such a prominent position to benefit my colleagues. It is difficult to find funding at the moment, especially for subjects which don't obviously have an immediate application for something that will make money.

"But the people who discovered magnetism and electricity had no idea what they could be used for. The MRI scanner wouldn't exist without particle physics. There are so many spin-off industrial investments in things that are being researched, and we need more of this."

There's only so far that one can run away with this. People "...who discovered magnetism and electricity..." had, in their corner, empirical evidence to at least tell them if they are on the right path or not. This is where the analogy to pursuing String Theory breaks down and the similarity ends. I don't believe that there has been, in the history of physics, a study in a field of physics that has gone for so long, and garnered THIS much attention, that has been totally devoid of any empirical evidence which indicates one way or the other that it is on a right path. For many of us who value physics as being guided by empirical evidence, this is the most troubling aspect of String theory.

Thursday, November 12, 2009

Oh well. This will be another hunt in the pursuit of finding any valid empirical evidence to show that String Theory is not a meaningless pursuit. Could String Theory produce a particle that has a lifetime of a minute?

Vafa traveled to CERN in late October to discuss with teams of scientists at the two main detectors on what else they might see. If the assumptions that he and Heckman make in the context of string theory are valid, Vafa said, the two lightest of the new particles are the gravitino and the stau. The gravitino, however, is so weakly interactive that it is hard to produce directly, Vafa said. A stau particle, however, is easier to produce and should be semi-stable, lasting as long as a minute. And it should leave a signature track — unexplainable by any of the already-observed particles — as it streaks across the LHC’s detectors.

I suppose this is OK for a popular media and for mass consumption for the public. The Telegraph has a rather amusing description of what the writer thinks as the 10 weirdest physics "facts". Of course, all the usual suspects are there: entanglement, superposition, speed of light, etc..

Still, can you nitpick a few rather inaccurate statements in there? I'm sure you can. I'm not going to bother because, really, it won't matter for those who don't understand physics, because the subtleties won't make a difference. Nevertheless, I wish that last part on "relativistic mass" didn't appear, because it will only propagate the same misconception that we are trying to eradicate (see here and here, for example).

WASHINGTON, D.C. — The Council of the American Physical Society has overwhelmingly rejected a proposal to replace the Society’s 2007 Statement on Climate Change with a version that raised doubts about global warming.

The Council’s vote came after it received a report from a committee of eminent scientists who reviewed the existing statement in response to a petition submitted by a group of APS members. The petition had requested that APS remove and replace the Society’s current statement. The committee recommended that the Council reject the petition.

The committee also recommended that the current APS statement be allowed to stand, but it requested that the Society’s Panel on Public Affairs (POPA) examine the statement for possible improvements in clarity and tone. POPA regularly reviews all APS statements to ensure that they are relevant and up-to-date regarding new scientific findings.

Appointed by APS President Cherry Murray and chaired by MIT Physicist Daniel Kleppner, the committee examined the statement during the past four months. Dr. Kleppner’s committee reached its conclusion based upon a serious review of existing compilations of scientific research. APS members were also given an opportunity to advise the Council on the matter. On Nov. 8, the Council voted, accepting the committee’s recommendation to reject the proposed statement and refer the original statement to POPA for review.

What this means is that the APS, which is the preeminent society of physicists in the US, and which tends to be extremely conservative in its policy and statements, continues to support the prevailing consensus of AGW model based on the scientifically available studies and results. The APS has never been known to choose something based on a whim or political pressure (refer to its statement on Missile Defense project). That is why many anti-AGW camp were quick to latch on to any possible hint that the APS might change its stance, because they know that this would be a major coup for an organization as respected as this one to show some doubt in this issue. Just look at the brouhaha when the APS Newsletter published a contradicting viewpoint to AGW a while back!

Alas, this is not to be the case here, and the APS's statement on AGW is extremely clear.

I'm a sucker for these type of analysis and article. It is a lot of fun to read when it isn't really connected to "significant" physics research, mainly because for me, it is a pleasant diversion from my work, but still intellectually stimulating. Furthermore, exercise like this can be something fun for a class or a group of students to do, because it is something they have seen or heard about, and it is based on really basic physics that they can do or follow along.

This is a preprint of a paper that will appear in AJP. It analyzes the mechanics of Usain Bolt's 100m sprints, both from the last Beijing Olympics in 2008, and the recent Track and Field Championship in 2009, both resulting in new world records.

Abstract: At the 2008 Summer Olympics in Beijing, Jamaican athlete Usain Bolt broke the world record for the 100 m sprint. Just one year later, at the 2009 World Championships in Athletics in Berlin he broke it again. A few months after Beijing, Eriksen et al. studied Usain Bolt's performance and predicted that the record could be about one-tenth of second faster, which was confirmed in Berlin. In this paper we extend the analysis of Ref. [1] to model Bolt's velocity profile for the Beijing 2008 and Berlin 2009 records. From the results we obtained, we were able to deduce the maximum force, the maximum power and the total mechanical energy produced by the athlete in both races. Surprisingly, we concluded that all of these values were smaller in 2009 than in 2008.

Oooh.. now that last part is, indeed, surprising. You have to read it to find out why! :)

Swear-by-it stories and anecdotal reports of benefit are one thing. Proving a treatment helps is quite another. Many alternative medicine studies have not included a placebo group — people who unknowingly get a dummy treatment so its effect can be compared.

Acupuncture is especially hard to research. Positive studies tend to lack comparison groups that have been given a sham treatment. Or they are often done in China, where the treatment is an established part of health care.

One U.S. study found that true acupuncture relieved knee arthritis pain better than fake acupuncture, in which guide tubes were placed but no needles were inserted. But a European study involving twice as many patients and using a more realistic sham procedure found the fake treatment to be just as good. The conclusion: Pain relief was due to the placebo effect.

The one bad thing about reports in mass media news like this is that they never give exact citation for all of these research and results that they are quoting. It's as if we are expected to just accept these things without having to know the source of what they used to draw up their conclusions.

Carter used a wonderful scientific vocabulary and showed some facts that were true.

However, blinded by science jargon, he put up facts and figures with little truth to them, no way to verify them (or if he did, they were not accurate and considered fraudulent in the scientific community), nor accuracy to the science actually used.

This man performed a wonderful show, and is an outstanding example of how the public will believe almost anything that has numbers and graphs in it with no scientific proof.

The writer listed several examples where Carter simply can't produce valid sources for his numbers.

I'm left to wonder how many people in the audience who bought into what they were told. We often talk about the public needed to be scientifically literate. What we mean by that is NOT that the public knows all these "facts", but rather, having the skill to analyze how one goes from A to B to C to D. How, for example, do you draw up the conclusion that, say, "gay marriage" leads to "undermining traditional marriage". People throw out those two phrases all the time, but no one seems to explain the mechanism that show how "gay marriage" CAUSES "undermining of traditional marriage". Not only that, if such mechanism exists, one needs to publish such a thing and be scrutinized for it by others who are experts in the field of study to ensure that such a mechanism is valid, and that leads to the unique conclusion.

The same thing is occurring here. One simply can't throw out all of these numbers and conclusions (something that is commonly done in politics and economics) without any basis to show that they are valid. But the public that isn't familiar with the scientific process are ignorant of that. This is why I'm very proud of this young writer who already has the skill (hopefully something he gained from his education) to analyze and question how such conclusions are made. So well done, Jim Eakins!

Making the public be scientifically literate should mean making them able to make a rational analysis of how one draws up a conclusion. It is why when I proposed a revamping of the undergraduate intro physics labs, I try to steer away from making "textbook tests" of physics principles. Rather, I focused on how one can draw up the conclusion on how A depends on B, and what is the exact relationship between those two. Our world has always been focused on how we can relate things, how are they interconnected, etc. These types of lab exercises precisely present such tests.

Monday, November 09, 2009

The major physics news of the day is certainly the passing of one of the giants in this field - Vitaly Ginzburg. Physics World has one of the best summary of his life and times.

My first introduction to the name "Ginszburg" was certainly when I took up superconductivity and came across the "Ginzburg-Landau" model for superconductivity. This may even be the first instance of the idea of the "order parameter" for superconductivity took shape. He certainly left a lot of marks in the world of physics.

There is a very good review of the current progress in the theory of Modified Newtonian Dynamics (MOND) in the current issue of Science[1].

Abstract: The observed matter in the universe accounts for just 5% of the observed gravity. A possible explanation is that Newton’s and Einstein’s theories of gravity fail where gravity is either weak or enhanced. The modified theory of Newtonian dynamics (MOND) reproduces, without dark matter, spiral-galaxy orbital motions and the relation between luminosity and rotation in galaxies, although not in clusters. Recent extensions of Einstein’s theory are theoretically more complete. They inevitably include dark fields that seed structure growth, and they may explain recent weak lensing data. However, the presence of dark fields reduces calculability and comes at the expense of the original MOND premise, that the matter we see is the sole source of gravity. Observational tests of the relic radiation, weak lensing, and the growth of structure may distinguish modified gravity from dark matter.

Whether you buy into it or not, this will at least get you up to speed on the strengths and weaknesses of this theory.

Friday, November 06, 2009

Here's a chance for you to learn about ski moguls, those "bump in the snow" thingies that you see on ski slopes that only make news during the Olympics, at least to me. I didn't realize there was a minor mystery to them till I read this.

Thursday, November 05, 2009

Scientists at the CERN particle physics laboratory in Geneva noticed that the system’s carefully monitored temperatures were creeping up.

Further investigation into the failure of a cryogenic cooling plant revealed an unusual impediment. A piece of crusty bread had paralysed a high voltage installation that should have been powering the cooling unit.

Oy vey!!!

Luckily, this isn't anything major, just a minor setback. But really, now small things like this will make the news. It means that they are on center stage and every little thing will get reported.

The American Association of Physics Teachers urges that every physics and astronomy department provide its majors and potential physics majors with the opportunities and encouragement to engage in a meaningful and appropriate undergraduate research experience.

There!

From my perspective, the "meaningful and appropriate" part of undergraduate research experience isn't just about doing "new" work or publishing some amazing discovery. That's just a bonus. What is more important is that the student learns the technique and procedure, and even more important, learns to think things through and be systematic in doing something. Those are skills that can only be acquired, not taught, and they transcend beyond just doing physics research. To me, those are the more important aspect out of doing research work that the student can acquire.

This discussion keeps popping up now and then. Recall that I've mentioned an article that suggests that throwing "granny style" might actually increase the chance of making a basket in basketball. Now comes another research on the mechanics of free-throw shooting that studies this a little bit more.

There is a difference though because the starting conditions are different, i.e. they're not studying the best way to do the free-throw, i.e. underhand or overhead.

The engineers used a men’s basketball for the study; it is heavier and a bit larger than basketballs used in women’s games. They also assumed that the basketball player doing the shooting was 6 feet 6 inches tall, and that he released the ball 6 inches above his head, so the “release height” was set to 7 feet. The free-throw line is 15 feet from the backboard, a cylinder-shaped opening that is 10 feet off the ground. Though it looks smaller, the diameter of a regulation basketball hoop is 18 inches; the diameter of a men’s basketball is a bit more than 9 inches.

So they are already starting with the assumption that one is launching the ball overhead.

Wednesday, November 04, 2009

I received a lot of flak when I made my blog entry on "An Astronomer At The Vatican", simply because I would have asked more pointed questions rather than the fluff that was given. What I wanted to established is specific and CLEAR stand of Catholicism in particular of various issues where religion and science have come to a loggerhead.

It is with that in mind that we have this example of someone who is using Christianity and are still arguing for creationism AND falsely claiming that evolution is wrong.

According to a presentation held Tuesday at West Virginia University, evolutionist Charles Darwin did not know geology, biology, or Jesus.

Dr. Robert Carter, has a doctorate in marine biology and is currently the head speaker and scientist for Creation Ministries International (USA) in Atlanta, Ga., gave a presentation listing in detail what Darwin did not know at that time. Carter argued evolution theory, therefore, cannot be held as the true explanation of the history of the natural world.

So you get all of these people who complained that my view of the Catholic belief is outdated, and yet you have on the other hand, various parts of the same Christian belief that clearly show that that "outdated" belief is alive and well. My question has always been, how come someone within the church (and I'm talking about ALL of Christianity, and not just a particular denomination) talk to this guy and set him straight, if that's possible? Obviously, he would not listen to other scientists since he has ignored not only the overwhelming evidence, but also the overwhelming consensus among scientists. But maybe he'll listen to someone with the same strong background in theology within his religion! If Catholics believe that evolution does not conflict with Catholicism, and if the Pope truly has declared that evolution is true, then someone's clearly wrong here! You guys are all reading from the SAME book, aren't you?

Tuesday, November 03, 2009

I'll sound like a broken record (how many would know that expression anymore?) but I'll say it again that condensed matter physics can be as "fundamental" as any area of physics. I've said this many times previously, and now we have another clear example of that.

This article reviews a recent paper that appeared in PRL. It appears that one can look at the superconducting phase transition in metal rings and gain quite an insight into the rapid cooling of our early universe.

Watching a metal transform into a superconductor, it may not be obvious that this transition provides access to some of the same physics that governed the cooling of the universe following the Big Bang. Yet at the root of both of these phenomena—albeit at astronomically different energy scales—is the question of how defects form in a continuous phase transition. In a paper appearing in Physical Review B [1], Roberto Monaco at the Università di Salerno in Italy, Jesper Mygind at the Technical University of Denmark, Ray Rivers at Imperial College London, UK, and Valery Koshelets at the Russian Academy of Science in Moscow have taken ideas about the early development of the universe and applied them to the dynamics of the superconducting phase transition in metal rings. In doing so, they introduce an elegant way to measure the tiny flux quanta that are trapped at the centers of these rings, and develop a new understanding of how the cooling process works in mesoscopic systems.

Monday, November 02, 2009

A group has claimed the detection of the reversed Cherenkov radiation in left-handed metamaterial. However, they didn't pass any charge particle through the metamaterial structure.

The second innovation is to emulate a charged-particle beam by means of a waveguide with a periodic array of slots, instead of using real charged particles [Fig. 1, right]. By doing so, Xi et al. solved the problem of extremely weak Čerenkov radiation in the microwave frequencies associated with moving charged particles. As an electromagnetic wave travels inside the waveguide, it emerges at each slot with a fixed phase retardation relative to the neighboring slots. This leaking radiation from the waveguide is equivalent to the radiation from a phased antenna array. The Fourier transform of the electric current carried by a moving charged particle results in a broad spectrum in the frequency domain. But as long as a single frequency is concerned, the current of the charged particle is equivalent to that of a phased dipole array, as mathematically proved by the authors. In this analog, the phase velocity of the electromagnetic wave propagating inside the waveguide corresponds to the moving speed of the charged particles in a regular Čerenkov radiation configuration.

In the experiment, the authors designed a waveguide with comparatively low refractive index of n ~0.5, which is equivalent to a charged particle moving with a speed twice as great as that of light in a vacuum. With this new experimental configuration, the radiation signal can be many orders of magnitude stronger than the traditional Čerenkov radiation induced by a fast charged-particle beam, and thus the Čerenkov radiation was directly observed along the backward direction within the left-handed frequency range of the metamaterials. It is worth noting that Grbic and Eleftheriades carried out an experimental attempt earlier at the University of Toronto, in which they observed the backward radiation from a low-index left-handed microwave transmission line into free space [8]. However, considering the fact that it is the phase velocity rather than group velocity of the electromagnetic wave propagating in the transmission line that corresponds to the speed of an equivalent moving charge, the Čerenkov radiation observed by Grbic et al. was indeed in the forward direction with respect to the direction of the equivalent moving charge.

I guess this is fine, but I'd say that one still needs to show this with actual particle beams. If this can't be done, then the claim that such phenomenon can be used as beam diagnostics doesn't quite hold.

Ironically, in the same issue of PRL, another paper gave a theoretical analysis of the detection of this reverse Cherenkov radiation of an electron beam passing into a left-handed metamaterial[1]. So it would be nice if one can actually detect this direction from electron beams, rather than simulated ones.

This is sort of a "trip report" of the 2009 Open House at Indiana University's Physics and Astronomy Dept. It sounds like a fun event, including an instruction on how to make a comet!

In the hands-on astronomy exhibit, my oldest son devoted about ten minutes to making a comet. Ingredients include: water, ammonia, dirt, corn syrup, and dry ice … plus some sarcasm and melodrama. A couple hours later, the comet didn’t look as pretty, but it retained enough mass to make it to our freezer. I fear this may be a summer snow ball accident waiting to happen.